Improve the series navigation links

Signed-off-by: Danila Fedorin <danila.fedorin@gmail.com>

layouts/partials/serieslink.html

@@ -4,7 +4,7 @@
     <div class="title-subtitle">
       {{ title .direction }} in Series
       {{ $divider := .term.Params.divider }}
-      {{ if $divider }}
+      {{ if (and $divider (strings.Contains .page.Title $divider)) }}
       {{ $rest := after 1 (split .page.Title $divider) }}
       <div class="title">{{ delimit $rest $divider }}</div>
       {{ else }}